Wear resistance of composite materials depends for instance on factors including concentration and sizes of reinforcing particles and on matrix properties. Under equal conditions additional increase of wear resistance is achieved through improvement of the properties of particles in the composite. Preparation of particles through ingot crushing leads to flaws, reed marks and other defects in particles that act as seats of destruction under the influence of loads. Thus in the prior art there is a need for an improvement of the microstructure of particles and consequently their mechanical properties.
SU 1802466 discloses a method of preparation of powder of refractory material which includes processing of bars with bar supply to the melting zone with a pusher mechanism, melting of bars with plasma, teeming of a liquid-alloy with plasma stream of a second plasmatron, to pan nodulizer and centrifugal atomization.
Disadvantages include that the technology requires greater current intensity of the plasma discharge and that the use of two plasmatrons makes the process of powder preparation much more expensive.
SU 503688 discloses an installation for preparation of spherical materials comprising a vacuum vessel with a rotary graphite crucible inside, with an inbuilt movable unmeltable tube wire which delivers powder.
SU 503688 shows a method of preparation of spherical materials which includes an electrical discharge between a rotary graphite crucible being an anode and a tungsten unmeltable sleeve cathode which delivers the original substance to the crucible heated under the action of electric arc. In the crucible there appears a liquid alloy which rises under the influence of centrifugal force, and is pushed out of the crucible, where after it flies and solidifies to drops and crystallizes in flight. The process is to be carried out in an inert-gas medium—argon.
Disadvantages include that the unmeltable electrode in the device doesn't make it possible to get optimal parameters of electric discharge, the current increases, on the edge of the crucible a hardened liquid-alloy mass is formed (so called “beard”) which leads to abnormality in the stability of the atomization process and frequent replacement of a crucible and, consequently, decrease of installation productivity and quality of the powder produced.
In the Journal of the Ukrainian SSR academy of sciences, No 72 (836), 1973 there is disclosed a method of producing a tungsten carbide alloy, with high hardness, strength and ductility.
RU 2301133 discloses a method and a device for preparation of refractory material powder, in particular cast tungsten carbide. The device comprises a rotatable crucible in a chamber in which the material is melted. Nitrogen is used as inert gas. Droplets are formed when the crucible rotates. Heating is provided by plasma arc discharge. The formation of a “beard” is avoided by moving the plasma stream. The heat output distribution from plasma can be varied from the edge of the crucible to the internal surface of the crucible in order to avoid the formation of beard.
In the prior art there is still a need to reduce the current of the plasma discharge required for melting the stock. There is also a need for an improved method to securely keep the liquid-alloy temperature higher than its melting point. There is also a need to reduce heat-losses, improve the homogeneity of the liquid-alloy and the homogeneity of the obtained powder.
Tungsten carbide alloy manufactured using conventional technology i.e. melting with subsequent crushing, has insufficient strength, due to presence of micro cracks.